1. Field of the Invention
The present invention generally relates to a resource allocation method and apparatus for a wireless communication system, and in particular, to a method and apparatus for transmitting/receiving an Acknowledgement (ACK)/Negative Acknowledgement (NACK) signal in a wireless communication system.
2. Description of the Related Art
In wireless communication systems, the technology for controlling a transmission error during data transmission is generally classified into a Forward Error Correction (FEC) technique and an Automatic Repeat reQuest (ARQ) technique. The FEC technique attempts to correct an error detected from received data, and decodes correct data upon success in the error correction. However, when the FEC technique has failed in the error correction, wrong information may be provided to users or the information may be missing. The ARQ technique transmits data using an FEC code having a high error detection capability, and when an error is detected from received data, a reception side sends a request for data retransmission to a transmission side.
The FEC technique has a relatively lower efficiency in a good channel environment, and reduces system reliability when the FEC technique fails in the error correction. On the contrary, the ARQ technique typically secures high system reliability and enables efficient transmission with a low redundancy, but the system reliability is considerably reduced in a poor channel environment due to the frequent retransmission request. In order to address such shortcomings, the two techniques have been appropriately combined to provide a Hybrid ARQ (HARQ) technique.
The HARQ technique basically attempts error correction on received coded data, referred to herein as a HARQ packet, and determines whether to make a retransmission request for the HARQ packet using a simple error detection code, such as a Cyclic Redundancy Check (CRC) code. A reception side of a system using the HARQ technique determines presence/absence of an error in a received HARQ packet, and transmits an HARQ Positive Acknowledgement (ACK) signal or an HARQ Negative Acknowledgement (NACK) signal to a transmission side according to the presence/absence of an error. The transmission side performs retransmission of the HARQ packet or transmission of a new HARQ packet according to the HARQ ACK/NACK signal. Upon normal receipt of an HARQ packet, the reception side transmits the ACK/NACK signal using appropriate resources. Particularly, when the HARQ technique is used, a channel over which the ACK/NACK signal is transmitted is called a Physical Hybrid ARQ Indicator Channel (PHICH).
An Orthogonal Frequency Division Multiplexing (OFDM)-based wireless communication system transmits the ACK/NACK signal on several subcarriers, and a Wideband Code Division Multiple Access (WCDMA) system transmits the ACK/NACK signal on a particular code channel. Generally, since packet data for several users is simultaneously transmitted in an arbitrary packet data transmission interval or Transmission Time Interval (TTI), ACKCHs for each of the HARQ packets are transmitted at particular times after the data received from the users which are scheduled data in the TTI is decoded.
Transmission of the ACKCH will be considered below separately for the downlink and the uplink. Regarding ACKCH for downlink data channels, each terminal or User Equipment (UE) that has received each of the data channels from a base station is allocated physical channel resources for transmitting the ACK/NACK signal from the base station, and transmits the ACKCH on the uplink. Meanwhile, regarding ACKCH for uplink data channels, after a base station receives the data channels from corresponding UEs, the base station transmits ACKCH for each data packet over the resources agreed upon between the base station and each UE.
FIG. 1 illustrates a conventional OFDM-based downlink frame structure of Enhanced Universal Terrestrial Radio Access (EUTRA) which is the next generation mobile communication standard of the 3rd Generation Partnership Project (3GPP). Referring to FIG. 1, a total of 50 Resource Blocks (RBs) 102 exist in a 10-MHz system bandwidth 101. One RB is composed of 12 subcarriers 103, and can have 14 OFDM symbol intervals 104. In every OFDM symbol interval 104, a modulation symbol of a downlink channel is transmitted on each subcarrier 103. As shown above, one subcarrier band in one OFDM symbol interval is referred to as a Resource Element (RE) 106, and in FIG. 1, a total of 168 (=14 OFDM symbols×12 subcarriers) REs exist in one RB. In one OFDM symbol interval 104, one downlink data channel can be allocated to one or more RBs according to a data rate, and can be transmitted through the allocated RBs.
With consideration of the downlink frame structure of FIG. 1, a maximum of 50 downlink data channels can be simultaneously scheduled in one TTI 105. In this case, the uplink needs 50 ACKCHs. Generally, a group of multiple REs 106 constitutes one ACKCH, and the overhead and performance occupied by the ACKCH in all resources of the system depends on how resources of the ACKCH are formed.
Therefore, in order to improve the overhead and performance occupied by ACKCH in all resources of the system, a need exists for a scheme for efficiently allocating and forming resources of the ACKCH.